To restore the default SMB2 you simply need to delete the newly created configuration file (nsmb.conf) with the command:

rm ~/Library/Preferences/nsmb.conf

Both workarounds force OS X to use SMB1 as a network protocol instead of the default SMB2 used by OS X 10.9 (Mavericks). While the first is an ad hoc solution the second is a persistent but reversible configuration change (for this user account). SMB1 is slower than SMB2 but stable.

[crarko adds: I don't have a way to test this at the moment, but I do recall reading that people have experienced some of these issues. If someone has a NAS device to test this with (especially if there have been problems) please let us know if either of these fixes helped.]

Do I need to restart or log out and back in after the changes? I have problems COPYING files to my SMB share since Mavericks! It won't let me copy because Finder tells me the files are still in use. Yes, that's COPYING (i.e. READING from the source, not moving, i.e. writing). This is ridiculous and Windows-like stupidity. Makes me want to go back to Linux...

If you have issues with "busy" files, try browsing in a view other than column view. I've found that the previews generated by the Finder in this view very often lead to "busy" files that cannot be easily cleared.

It's probably the preview pane that would be causing it then. I use column view all the time, but I have the preview pane unchecked. I'm finding 10.9 to be faster and more stable than 10.8, sometimes on 10.8, finder would revert to the root instead of the previous folder when I was deleting stuff, it works great in 10.9. I use smb://(server) to connect to our old Buffalo NAS.

Finally bit the bullet and tried this. The performance difference on my system is amazing! Mid-2010 Mac mini running Mavericks, using Graphic Converter to browse photos on an Iomega NAS (connected via Ethernet to the same switch the Mac is using). Original performance was so poor that I copied photos to the local drive for browsing, instead of using the NAS! Made the change listed here today, and using GC to browse the NAS feels just as fast as the local drive!

Thanks for this information which I found when trying to solve a problem saving .DOCX files from Office for Mac 2011 to file shares on a Windows Server 2012.

There was also a possible hint from http://word.mvps.org/Mac/CantSaveToServer.html which I'd also tried.

In the end I believe the issue lies with and incompatibility between AVG Anti Virus for Mac (and its real time protection), Office 2011 for Mac and Windows Server, turning this off seemed to solve the problem - more testing required.